Phytoforensics: Applications in vapor intrusion assessment

Vapor intrusion (VI) occurs when contaminants in the vapor phase migrate in the shallow subsurface and enter buildings through cracks, seams, and gaps and has been recognized as a serious human-health threat as occupants are exposed to potentially harmful concentrations over long periods of time. The VI pathway has recently (2017) been identified as a primary exposure pathway and implemented into the Hazard Ranking System for inclusion on the Nation Priorities List. However, assessing VI and human exposure is not simple and current methods are time-, cost-, and labor-intensive; intrusive; and temporally and spatially variability. Trees are ideal candidates for environmental biomonitors because they are ubiquitous, active samplers of vapor and groundwater and because they are thought to sample over large spatial and temporal scales, effectively averaging variability. Sampling trees is noninvasive and does not require the construction of sampling ports in homes, increasing the likelihood of obtaining property access and VI data. Tree samples are representative of the shallow subsurface with a footprint similar to a residential building. Directional tree sampling can also be used to elucidate shallow subsurface contamination from a single tree, and tree sampling is shown to be correlated with VI samples, especially when environmental samples are averaged over months and years. However, non-uniform distributions of tree-core samples likely resulted in large interpolation error in areas where trees are sparse. Although these findings demonstrate that tree sampling can augment traditional VI assessment methods, tree sampling is best applied as a screening tool because of the many parameters, and their associate uncertainties, that control mass transfer of contaminants in the subsurface and entry into plants and the built environment --Abstract, page iv